dinit/BUILD

Building Dinit
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Building Dinit should be a straight-forward process. It requires GNU make and a C++11 compiler
(GCC version 4.9 and later, or Clang ~5.0 and later, should be fine)

On the directly supported operating systems - Linux, OpenBSD, FreeBSD and Darwin (macOS) - a
suitable build configuration is provided and will be used automatically if no manual configuration
is supplied - skip directly to running "make" (more details below) if you are on one of these
systems and are happy to use the default configuration.

For other systems, or to fine tune or correct the configuration, create and edit the
"mconfig" file (start by copying one for a particular OS from the "configs" directory) to choose
appropriate values for the configuration variables defined within. In particular:

  CXX     : should be set to the name of the C++ compiler (and link driver)
  CXXOPTS :  are options passed to the compiler during compilation (see note for GCC below)
  LDFLAGS :  are any extra flags required for linking; should not normally be needed
             (FreeBSD requires -lrt).

Note that the "eg++" or "clang++" package must be installed on OpenBSD as the default "g++"
compiler is too old. Clang is part of the base system in recent releases.

Then, from the top-level directory, run "make" (or "gmake" if the system make is not GNU make,
such as on most BSD systems):

    make

If everything goes smoothly this will build dinit, dinitctl, and optionally the shutdown
utility. Use "make install" to install; you can specify an alternate installation by
setting the "DESTDIR" variable, eg "make DESTDIR=/tmp/temporary-install-path install".


Recommended Compiler options
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Dinit should generally build fine with no additional options, other than:
 -std=c++11 :  may be required to select correct C++ standard.
 -D_GLIBCXX_USE_CXX11_ABI=1 :   see "Special note for GCC/Libstdc++", below. Not needed for
                                most modern systems.

Recommended options, supported by at least GCC and Clang, are:
 -Os       : optimise for size
 -fno-rtti : disable RTTI (run-time type information), it is not required by Dinit.
             However, on some platforms such as Mac OS (and historically FreeBSD, IIRC), this
             prevents exceptions working correctly.
 -fno-plt  : enables better code generation for non-static builds, but may cause unit test
             failures on some older versions of FreeBSD (11.2-RELEASE-p4 with clang++ 6.0.0).
 -flto     : perform link-time optimisation (option required at compile and link).

Consult compiler documentation for further information on the above options.


Other configuration variables
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There are a number of other variables you can set in the mconfig file which affect the build:

SBINDIR=...
    Where the "/sbin" directory is. Executables will be installed here.
MANDIR=...
    Where the "man" directory is. Man pages will be installed here.
SYSCONTROLSOCKET=...
    Default full path to the control socket, for when Dinit runs as system service manager.
BUILD_SHUTDOWN=yes|no
    Whether to build the "shutdown" (and "halt" etc) utilities. These are only useful
    if dinit is the system init (i.e. the PID 1 process). You probably don't want this
    unless building for Linux.
SHUTDOWN_PREFIX=...
    Name prefix for "shutdown", "halt" and "reboot" commands (if they are built). This affects
    both the output, and what command dinit will execute as part of system shutdown.
    If you want to install Dinit alongside another init system with its own shutdown/halt/reboot
    commands, set this (for eg. to "dinit-").
USE_UTMPX=1|0
    Whether to build support for manipulating the utmp/utmpx database via the related POSIX
    functions. This may be required (along with appropriate service configuration) for utilities
    like "who" to work correctly (the service configuration items "inittab-id" and "inittab-line"
    have no effect if this is disabled). If not set to any value, support is enabled for certain
    systems automatically and disabled for all others.
SANITIZE_OPTS=...
    Any options to enable run-time sanitizers or additional safety checks. This will be used
    only when building tests. It can safely be left blank.


Running test suite
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Build the "check" target in order to run the test suite:

    make check

The standard mconfig options enable various sanitizers during build of the tests. On Linux you may
see an error such as the following:

    make[3]: Leaving directory '/home/davmac/workspace/dinit/src/tests/cptests'
    ./tests
    ==25332==ERROR: AddressSanitizer failed to allocate 0xdfff0001000 (15392894357504) bytes at
    address 2008fff7000 (errno: 12)
    ==25332==ReserveShadowMemoryRange failed while trying to map 0xdfff0001000 bytes. Perhaps
    you're using ulimit -v
    make[2]: *** [Makefile:12: run-tests] Aborted

If you get this, either disable the address sanitizer or make sure you have overcommit enabled:

    echo 1 > /proc/sys/vm/overcommit_memory 

Any test failures will abort the test suite run immediately.

To run the integration tests:

    make check-igr
    
(The integration tests are more fragile than the unit tests, but give a better indication that
Dinit will actually work correctly on your system).

In addition to the standard test suite, there is experimental support for fuzzing the control
protocol handling using LLVM/clang's fuzzer (libFuzzer). Change to the `src/tests/cptests`
directory and build the "fuzz" target:

    make fuzz

Then create a "corpus" directory and run the fuzzer:

    mkdir corpus
    ./fuzz corpus

This will auto-generate test data as it finds input which triggers new execution paths. Check
libFuzzer documentation for further details.


Installation
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You can install using the "install" target:

    make install

If you want to install to an alternate root (eg for packaging purposes), specify that root via
DESTDIR:

    make DESTDIR=/some/path install

The dinit executable will be put in /sbin (or rather, in $DESTDIR/sbin), which may not be on the
path for normal users. Consider making a symbolic link to /usr/sbin/dinit.


Special note for GCC/Libstdc++
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(Note: the issue discussed here has apparently been resolved in recent GCC versions).

GCC 5.x onwards includes a "dual ABI" in its standard library implementation, aka Libstdc++.
Compiling against the newer (C++11 and later) ABI can be achieved by adding
-D_GLIBCXX_USE_CXX11_ABI=1 to the compiler command line; this uses a non-standard language
extension to differently mangle symbol names in order to link against the new ABI versions.

(Some systems may be configured to build with the new ABI by default, and in that case you
build against the old ABI using -D_GLIBCXX_USE_CXX11_ABI=0).

This is problematic for several reasons. First, it prevents linking against the new ABI with
other compilers that do not understand the language extension (LLVM i.e. clang++ does so
in recent versions, so this is perhaps no longer much of a problem in practice). Secondly,
some aspects of library behaviour are ABI-dependent but cannot be changed using the ABI
macro; in particular, exceptions thrown as a result of failed I/O operations are, in GCC
versions 5.x and 6.x, always "old ABI" exceptions which cannot be caught by code compiled
against the new ABI, and in GCC version 7.x they are always "new ABI" exceptions which cannot
be caught by code compiled against the old ABI. Since the one library object now supposedly
houses both ABIs, this means that at least one of the two ABIs is always broken.

A blog post describing the dual ABI mechanism can be found here:

    https://developers.redhat.com/blog/2015/02/05/gcc5-and-the-c11-abi/

The bug regarding the issue with catching other-ABI exceptions is here:

    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66145

Since Dinit is affected by this bug, the unfortunate possibility exists to break Dinit by
upgrading GCC. If you have libstdc++ corresponding to GCC 5.x or 6.x, you *must* build with
the old ABI, but Dinit will be broken if you upgrade to GCC 7. If you have libstdc++ from
GCC 7, you *must* build with the new ABI. If the wrong ABI is used, Dinit may still run
successfully but any attempt to load a non-existing service, for example, will cause Dinit
to crash.